diff --git a/README.md b/README.md
index 1179fb49..6ddeaa83 100644
--- a/README.md
+++ b/README.md
@@ -298,13 +298,26 @@ That function will have state while `stream = true` is used.
 
 ### `@exodus/bytes/bigint.js`
 
+Convert between BigInt and Uint8Array
+
 ```js
 import { fromBigInt, toBigInt } from '@exodus/bytes/bigint.js'
 ```
 
 #### `fromBigInt(bigint, { length, format = 'uint8' })`
+
+Convert a BigInt to a Uint8Array or Buffer
+
+The output bytes are in big-endian format.
+
+Throws if the BigInt is negative or cannot fit into the specified length.
+
 #### `toBigInt(arr)`
 
+Convert a Uint8Array or Buffer to a BigInt
+
+The bytes are interpreted as a big-endian unsigned integer.
+
 ### `@exodus/bytes/hex.js`
 
 Implements Base16 from [RFC4648](https://datatracker.ietf.org/doc/html/rfc4648)
diff --git a/bigint.d.ts b/bigint.d.ts
new file mode 100644
index 00000000..a0758f99
--- /dev/null
+++ b/bigint.d.ts
@@ -0,0 +1,48 @@
+/**
+ * Convert between BigInt and Uint8Array
+ *
+ * ```js
+ * import { fromBigInt, toBigInt } from '@exodus/bytes/bigint.js'
+ * ```
+ *
+ * @module @exodus/bytes/bigint.js
+ */
+
+/// <reference types="node" />
+
+import type { OutputFormat, Uint8ArrayBuffer } from './array.js';
+
+/**
+ * Options for converting BigInt to bytes
+ */
+export interface FromBigIntOptions {
+  /** The length in bytes of the output array */
+  length: number;
+  /** Output format (default: 'uint8') */
+  format?: OutputFormat;
+}
+
+/**
+ * Convert a BigInt to a Uint8Array or Buffer
+ *
+ * The output bytes are in big-endian format.
+ *
+ * Throws if the BigInt is negative or cannot fit into the specified length.
+ *
+ * @param x - The BigInt to convert (must be non-negative)
+ * @param options - Conversion options
+ * @returns The converted bytes in big-endian format
+ */
+export function fromBigInt(x: bigint, options: { length: number; format?: 'uint8' }): Uint8ArrayBuffer;
+export function fromBigInt(x: bigint, options: { length: number; format: 'buffer' }): Buffer;
+export function fromBigInt(x: bigint, options: FromBigIntOptions): Uint8ArrayBuffer | Buffer;
+
+/**
+ * Convert a Uint8Array or Buffer to a BigInt
+ *
+ * The bytes are interpreted as a big-endian unsigned integer.
+ *
+ * @param arr - The bytes to convert
+ * @returns The BigInt representation
+ */
+export function toBigInt(arr: ArrayBufferView): bigint;
diff --git a/package.json b/package.json
index 3fa2d797..17e3bdd9 100644
--- a/package.json
+++ b/package.json
@@ -90,6 +90,7 @@
     "/base64.d.ts",
     "/bech32.js",
     "/bigint.js",
+    "/bigint.d.ts",
     "/encoding-browser.js",
     "/encoding-browser.browser.js",
     "/encoding-browser.native.js",
@@ -140,7 +141,10 @@
       "default": "./base64.js"
     },
     "./bech32.js": "./bech32.js",
-    "./bigint.js": "./bigint.js",
+    "./bigint.js": {
+      "types": "./bigint.d.ts",
+      "default": "./bigint.js"
+    },
     "./hex.js": {
       "types": "./hex.d.ts",
       "node": "./hex.node.js",